From a holistic point of view, we can approach neuroscience from thousands of years back in the history of humankind from the perspective of those elements associated with macroscopic neuroanatomy. Neural science has been recognized as the study initiated more than a hundred years ago through the microscopic analysis of the neural cell units of the nervous system. Neuroscience has become enriched from other disciplines, which have been incorporated into it as an integrated set of macroscopic, microscopic, physical and molecular knowledge focusing on very selective topics from the neuroscientific perspective. Functional neuroanatomy, it can be argued, bridges neuroscience and neural science.
The study of the brain has been the province of several disciplines, among them neuropsychology, which has used the lesion method to determine localization by observing the absence of function after injury, whereas neuroanatomy and neurobiology have mapped neural development and connectivity and have studied functionality in animal models. The boundaries between all these disciplines have become steadily less distinct, thus, giving birth to the broad discipline known as cognitive neuroscience (Andreasen, 1997). Thus, Neurosciences owes its name to the enrichment it has obtained from various areas of knowledge (Duque-Parra, 1999).
Neurosciences (because of their integrating quality of several sciences associated with neurology), or simply Neuroscience, is a term that reflects the truly interdisciplinary nature of modern brain research (Beatty, 1995). Particularly in the realm of neuroscience, neural science aims at understanding the biological mechanisms that account for mental activity (Albright et al., 2000). Neuroscience differentiates itself from other cognitive sciences, because it can enunciate unequivocally its questions and verify whether there is any progress leading to its answers, thus building the best explanatory bridges between the neurochemical and the neural levels, going through the macroscopic level, and becoming more complex in the explanation of perception and memory, among other aspects (Duque-Parra, 2001).
Neuroscience is a term that reflects the truly interdisciplinary nature of modern brain research.
NEUROSCIENCE THROUGH THE AGES
Elements associated with neuroscience have been reported throughout history. In Egyptian culture, an old fact determines a link between mental processes and the word used to denominate the encephalon, according to Edwin Smith's Papyrus which dates back to the 17th century B.C. The symptoms, diagnosis, and prognosis of two people with wounds in the head are described in that document (Kandel et al., 1997). The importance of the brain was well appreciated in this document where there is a quotation with reference to the sensation of throbbing and fluttering beneath the fingers when palpating the exposed surface of the living brain in an injured individual.
The Papyrus also refers to the effects of a brain injury on motor functions, thus affirming that the results were seen to be different depending on which side the injury was located (Lyons and Petrucelli, 1978). In the same Egyptian culture, between 3,000 and 2,500 B.C., physicians used to speak about head injuries with loss of speech, according to some documented notes found in a papyrus dealing with surgery, which was deciphered by Breasted. The Egyptian surgeons believed that the speech loss resulted from “something that came in from the outer side,” something such as “the breath of a god or of death,” and that the patient “became mute within his sorrow” (Jenkins et al., 1976). This written document shows the evidence of a relation between the content of the head (the encephalon and its annexes) with somatic structures associated with several forms of aphasia. Despite these initial concepts on the association between encephalon and speech, for the majority of Egyptian physicians, the heart was the seat of knowledge. That was why the deterioration of intellect was attributed to blood clotting in the heart cavities, an aspect stated in the Ebers's papyrus (Pardo, 1987).
Accordingly, the functions associated with thinking depended on the heart, an idea that was shared by Aristotle in the fourth century B.C. (Lhermitte, 1940; Pines, 1973; Canguilhem, 1997). Hippocrates, in his treatise about the holy disease (epilepsy) (Canguilhem, 1997; Blits, 1999) stood his ground for an opposite perspective in the fifth century B.C., as he taught that the brain was the home of sensations, the organ of motion and judgment (Lhermitte, 1940; Canguilhem, 1997). Hippocrates stated: “Men and women must realize that our pleasure and happiness, our sorrows and tears come from the brain and only from the brain. It is because of the brain that we think, see, hear, and differentiate beauty and ugliness, good and evil, pleasure and displeasure. It is also because of the brain that we may become crazy and delirious, terrified or insomniac, anguished or incoherent; these events take place when the brain sickens because of an excess of heat or cold, humidity or dryness, or because of any other antinatural event to which the brain is not used to” (Rosselli, 1993; Eisenberg, 1995). Hippocrates also stated, “I assure that the brain is the most powerful organ in the human body: eyes, ears, tongue, hands, and feet act according to its discernment; it is the interpreter of consciousness” (Ramón y Cajal, 1999).
Another Greek wise man that contributed to the knowledge of the brain was Alcmaeon of Croton (c. 500 B.C.), who having traced the main sensory nerves to the brain, considered it the seat of sensation and intellect (Lhermitte, 1940; Blits, 1999). He also speculated that sleep occurred when the blood vessels in the brain were commonly full of blood and that when blood quit the brain, wakefulness appeared; he also criticized the accepted belief of the time that semen originated in the brain (Lyons and Petrucelli, 1978). Two points of view coexisted in Democritus, he located thinking or intelligence in the brain, anger in the heart, and desire in the liver (Lopera, 1997).
In Greco-Roman times it was a common belief that the body was animated by a gaseous spirit located in the cerebral ventricles, a spirit that reached the periphery through the nerves, which, at the same time, were considered hollow; an idea that was faithfully supported by Descartes (Lhermitte, 1940; Clarck, 1966). The idea that the cerebral ventricles or, more precisely, the cerebrospinal fluid, are the material substrate to the psychic processes lasted for 1,500 years. This idea was supported by authorities such as Andreas Vesalius and by Soemmering, who stated that the actual substrate for psychic processes was the animal spiriti that flow through the nerves (Luria, 1977). This flow of ideas, opposite in some historical moments, revisited to a certain extent, the second Egyptian concept mentioned above. Much later in Europe, it was believed that the brain was no more than a bag of mucus and that when somebody got a bad cold and had a runny nose, that flow was part of the cerebral mucus distilled into the nose through small openings located at the bottom of the brain (Nathan, 1972).
Until the middle of the 19th century, gross dissection was the primary tool available to scientists to study the nervous system (Ralston, 1998). Due to the lack of appropriate tools to study the nervous system, considerations centered on the macroscopic aspects. Indeed, neurohistology (Fig. 1) remains a critical aspect of modern-day investigations. But just at the end of the 19th century, the nervous tissue and its composition became a solid scientific topic (Rose, 1972).
As the knowledge about the smallest structural units associated with the nervous system increased, Deiters, in 1865, pictured the nerve cell almost similarly as it is described today: with its soma prolonged into the dendrites and axon; but by 1870, the idea that the nerve cells formed a continual network that extended through the white matter and the spinal cord predominated. This concept was the thought of those who defended the reticular theory, initially submitted by Gerlach in 1858 (Ramón y Cajal, 1999), which let him structure his reticular theory of the continuity of the nervous system (Williams and Warwick, 1992).
MODERN NEURAL SCIENCE
Modern neural science, as we know it today, began at the turn of the 20th century when Santiago Ramón y Cajal provided the critical evidence for the neuron doctrine; the idea that neurons served as the functional signaling units of the nervous system and that neurons connected to one another in precise ways. Ramón y Cajal's view of the neuron doctrine represented a major shift in emphasis to a cellular view of the brain (Albright et al., 2000). He used a specialized silver staining method developed by Camilo Golgi that labeled only an occasional neuron (Ramón y Cajal, 1999; Albright et al., 2000). This entire labeling of the neuron permitted the visualization of its cell body, its dendritic tree, and its axon (Fig. 2). Many believed that the cytoplasm of two opposite cells was continuous at their points of contact and formed a syncytium or reticular net. This confusion was solved indirectly by Ramón y Cajal in the 1890s and definitely in the 1950s by Palay and Palade (Duque-Parra, 1997; Albright et al., 2000) and by De Robertis and Bennett (Williams and Warwick, 1992; De Robertis et al., 2000).
The use of the electron microscope to reveal the structure of the synapse (Duque-Parra, 1997; Ralston, 1998) finally settled the old argument between those who viewed the nervous system as a syncytium and those who considered it to consist of individual cells (Ralston, 1998). It is known that Cajal mastered and further refined Golgi's silver impregnation method (with whom he would share the Nobel Prize in 1906) and exploited this technique in an exhaustive series of studies on the nervous system (Haines, 1999; Ramón y Cajal, 1999).
The advent of microscopic methods in the 19th century permitted the careful examination of the developing brain and the spinal cord. The application of methods of electrical stimulation allowed investigators to start understanding the interrelationships between structure and function of the nervous system (Ralston, 1998). In the 20th century, the development of a common language among neurobiologists was initially approached through a series of lectures on the Brain Sciences (Rose, 1972), such as the Symposium on “Cerebral Mechanisms and Consciousness,” in 1952 organized by the International Council of Organisms on Medical Sciences (UNESCO-WHO) (Fernández-Guardiola, 1979) and that organized by UNESCO in 1968 (Rose, 1972). Neuroanatomy and neurophysiology were, until the mid-1900s, the most developed branches of health sciences and those that contributed the most to widening the knowledge about the structure and functioning of the nervous system. It was not possible yet to talk about consolidated Neuroscience, because there was a large gap among the physiological findings and their structural grounding.
The development of chemical-biological, electronic computing, and imaging techniques in the second half of the 20th century built the bridge that neuroanatomists and neurophysiologists were longing for. From the 1960s onward, it has been possible to speak about neuroscience as a set of sciences through which we look into the brain; some of these sciences play a starring role with reference to the challenges proposed by the brain (Hernández-Mesa, 1996).
Functional neuroanatomy is a sine qua non element for the appearance of neural science and neuroscience.
Current neuroscience differs from other cognitive sciences as it can enunciate its questions more unequivocally and verify whether it advances or not on the search of its answers, thus building better explanatory bridges between the neurochemical and neural levels, taking into account the macroscopic issue and becoming more complex with regard to the explanation of perception and memory among others (Duque-Parra, 2001). Neural scientists have opted for a reductionist approach to analyze the nervous system, although some authors think that the holistic approach had its first success in the middle of the 19th century with the analysis of the behavioral consequences after selective injuries of the brain (Albright et al., 2000). In the past two decades, experimental methods such as axon transport, gene expression, and synthesis of neurotransmitters and their receptors have provided major advances in our understanding of the functioning of the brain and have contributed to increase our knowledge about the organization of the nervous system (Ralston, 1998).
DISCUSSION OF TERMS
The terms neuroscience and neural science may provide a comparison framework as they look identical, because the first comprises the second. Neural Science was born approximately a century ago and focuses on the study of the neuron as the structural and functional element of communication in the nervous system. Neuroscience includes neuroanatomy, neurophysiology, comparative neuroanatomy, neuroimagery, molecular biology, and other sciences, some of them developed in ancient times and others in recent times. Accordingly, neuroscience, as a construction of knowledge, developed in the course of the past 50 years.
It has been established that in ancient times, such as those of the pharaohs more than 3,000 years ago, our ancestors in various parts of the world had a goal with neuroscience, with reference to the historical moment, consisting of understanding the biological mechanisms that account for mental activity. It could be argued that biology had not appeared as it is today, but from the perspective of the conceptualization of macroscopic anatomy, it was evident that biological functions and mechanisms were studied, thus, comparing the brain with the heart. As a matter of fact, it can be deduced that functional neuroanatomy is a sine qua non element for the appearance of neural science and neuroscience, which accounts for the condition of mother and daughter science.
Neural Science dates back to more than a century ago, but the study concerning behavior—the birth of neuroscience—goes back to the earliest of times. In our time, a surprising avalanche of machinery and technology has been used in the transdisciplinary and interdisciplinary study of the nervous system, thus becoming an extension of our senses a more complete understanding of such a complex system.
Although I have highlighted instances in which studies associated with Neuroscience reach into the ancient past, modern neuroscience, as such, started approximately a century ago, through advances in functional neuroanatomy that also gave rise to neural science. The antecedents of neural science, therefore, go back to such distant epochs as those of the pharohs and the Greek masters, as well as the works of Deiters, Cajal, and other fundamental contributors to the birth of Neural Science proper. Accordingly, it can be said that some concepts of neural science date back beyond 100 years, but as a scientific entity dealing with criteria relative to the neuron taken as a structural and functional unit of the nervous system, Neural Science is really only around 50 years old—the daughter of Functional Neuroanatomy and grand-daughter of Neuroscience.
Dr. Duque-Parra is the Director of the Program of Basic Sciences for Health, Professor of Anatomy at the Medicine Program at the School of Health Sciences of the University of Caldas, and Professor of Neurophysiology at the Program of Physical Therapy at the Autonoma University of Manizales, Colombia, South America. He can also be found at the Laboratorio Andaluz de Biologia, Universidad Pablo de Olavide, Spain.